Heat exchange of bypass air feed with liquid product



Dec. 19, 1967 J MINKHORST ET AL 3,358,462

HEAT EXCHANGE OF BYPASS AIR FEED WITH LIQUID PRODUCT 4 Sheets-Sheet 1 Filed Oct. 29, 1964 III/IIII 71/1 ZFII IIIII IIIIII FIGS INVENTORS JAN H. MIN/(HORST HERMAN F- MAR! BY j \v ATTORNEYS D60 1967 J. H. MINKHORST ET AL 3,358,462

HEAT EXCHANGE OF BYPASS AIR FEED WITH LIQUID PRODUCT Filed 001.. 29, 1964' 4 Sheets-Sheet 2 I I I 6|: I i y 43- fin 46 33 64} Jl II [I i i I l i I ,l l l I I 4 J5 31 g I I 1 I as 52 i E l t v V ,.*---se 63- Y I i E i 62 I 6 FIG.5 L 67f ATTORNEYS Dec. 19, 1967 J. H. MINKHORST ETAL 3,358,462

HEAT EXCHANGE OF BYPASS ,AIR FEED WITH LIQUID PRODUCT Filed Oct. 29, 1964 4 Sheets-Sheet 3 I I 9 6L Q. I- 1 'LI'IIIIIIIITII 39 r |l Z I I J 1 I 5Q I I I I k I I I i 55 3| I I i l l. I I v I g Y F IG.6 67[ I, INVENTORS JAN H MiNKHoRsr HERMAN F. NARis' BY "M ATTORNEYS Dec. 19, 1967 Filed Oct. 29, 1964 J. H. MINKHORST ET AL 3,358,462

HEAT EXCHANGE OF BYPASS AIR FEED WITH LIQUID PRODUCT 4 Sheets-Sheet 4 /I I 5 W (O) i l I i 52. f l g i i I -55 z I v I 63", v v

PIC-3.7 53

INVENTORS JAN H. HiNKHoRs-r HERMAN F- MAM:-

BY 904444- Y ATTORNEYS United States Patent 3,358,462 HEAT EXCHANGE OF BYPASS AIR FEED WITH LIQUID PRODUCT Jan H. Minkhorst, Meander 1035, Amstelveen, Netherlands, and Herman F. Maris, Turfpoorstraat 39, Naarden, Netherlands Filed Oct. 29, 1964, Ser. No. 407,409 9 Claims. (Cl. 62-37) The invention relates to a system for the separation by fractionation of a gas mixture, e.g. air, in its components, said system comprising a gas fractionating column. Provided in said column is an evaporator-condenser, in which at least one of the products is in thermal contact with the other product or with the mixture to be separated, and said system being provided for the supply of the required amount of cold with at least one cold-gas-refrigerator. Furthermore the system comprises at least one heat-exchanger, in which at least part of the gas mixture to be separated can be brought into thermal contact with the products leaving the system in the gaseous state.

In known systems of the kind referred to the components leave the system in the gaseous or the liquid state. A disadvantage of these systems is that it is not possible to withdraw in a simple manner one or both components either in the gaseous state or in the liquid state or in both these states in any desired ratio from the system.

The system according to the invention has the object to avoid the above-mentioned disadvantage in a favourable way and to that end it is characterized in that the arrangement of the system is such as to allow at least one of the products which in the evaporator-condenser are in thermal contact with one another to be withdrawn from the system either in the liquid state or in the gaseous state or in both these states, to which end the system comprises a cooler-evaporator, in which the part of the gas mixture to be separated which has not passed through the heatexchanger can be cooled by condensate of one or more of the products, said cooler-evaporator being supplied through a liquid conduit with liquid from one of the liquid containers of the condenser-evaporator and being connected by a vapour conduit to the vapour space of the relevant container.

It is certainly possible in practice to arrange the coolerevaporator and the condenser-evaporator of the column separately. However, in such an arrangement the coolerevaporator must be provided with a heat transmitting wall, through which the two products are in thermal contact with one another, so that in that case the cooler-evaporator has the same structure as a condenser-evaporator of a column. When in accordance with the invention the task of the cooler-evaporator and the task of the condenser-evaporator of the column are combined the condenser-evaporator-part of the cooler-evaporator can be entirely dispensed with. Thereby a considerable structural simplification of the construction is obtained, whereas by a conveniently chosen arrangement of the refrigerator, the cooler-evaporator and the condenser-evaporator of the column surprising additional advantages are obtained, which will be hereinafter elucidated.

A favourable embodiment of the system according to the invention is characterized in that the cooler-evaporator communicates through a liquid conduit with the liquid-evaporator-container of the condenser-evaporator and further in that a conduit connecting the cooler-evaporator with the vapour space of the evaporator-container of the condenser-evaporator opens into the upper part of the cooler-evaporator and a condensation space which surrounds the cold head of the cold-gas-refrigerator communicates with the condensation space of the condenserevaporator.

This embodiment has the advantage that the cold-gasrefrigerator condenses the component having the lowest boiling point, while said component is exposed to a raised pressure. Thereby condensation takes place at a temperature, which is higher than that of the boiling point of the said component at atmospheric pressure. Consequently, the refrigerator delivers its cold at a higher temperature, at which temperature the refrigerator operates with a more favourable useful effect.

In the case in which the gas mixture to be separated is air, the refrigerator will in this embodiment of the invention condense the nitrogen, so that should hydrogen leak out of the refrigerator fire is not to be feared.

In a further favourable embodiment of the system according to the invention a condensation space surrounding the cold head of the cold-gas-refrigerator communicates with the vapour space of the evaporator-container of the condenser-evaporator. In this case the cold-gas-refrigerator condenses the component with the higher boiling point.

Still another favourable embodiment of the system according to the invention has the feature that the coolerevaporator communicates through a liquid conduit with a liquid collecting container provided in the condensation space of the condenser-evaporator and is further characterized in that a vapour conduit connecting the coolerevaporator with the vapour space in the condensation space of the condenser-evaporator opens into the upper part of the cooler-evaporator and a condensation space surrounding the cold head of the cold gas-refrigerator communicates with the condensation space of the condenser-evaporator.

Another embodiment of the system according to the invention is characterized in that the cooler-evaporator communicates through a liquid conduit with a liquid collecting container provided in the condensation space of the condenser-evaporator and further in that a vapour conduit connecting the cooler-evaporator with the vapour space in the condensation space of the condenser-evap orator opens into the upper part of the cooler-evaporator and a condensation space which surrounds the cold head of the cold-gas-refrigerator communicates with the vapour space of the evaporator-container of the condenserevaporator.

A favourable embodiment of the system according to the invention has the feature that the system comprises a control device adapted to vary the output of the coldgas-refrigerator and the ratio between the medium flows in the system at a variation of the amount of discharged liquid of one of the products such as to keep the heatexchangers balanced and the ratio of the medium flows in the column at the right value, that means at the value at which the right liquid levels in the column are maintained.

A further embodiment of the system according to the invention is characterized in that provided in the evaporator-space of the condenserevaporator is an indicator for the liquid level which is connected through a control device With the cold-gas-refrigerator, said control device operating such as to have the output of the cold-gas-refrigerator increased at a fall of said level. In this way the liquid level in the condenser-evaporator is continuously kept constant when the discharged amounts of liquid are varied.

A favourable embodiment of the system according to the invention is further characterized in that at a variation of the amount of discharged liquid of one of the products the control device varies the amount of discharged gas of said product such as to keep the sum of the amount of discharged liquid and the amount of discharged gas of said product constant.

The invention will be further elucidated with the aid of the accompanying drawing, in which some possible embodiments of gas separating systems according to the invention are diagrammatically illustrated. i i

In FIGS. 1 to 4 inclusive the condenser-evaporator-part how the refrigerator, the cooler-evaporator and the condenser-evaporator of the column may be arranged with respect to one another.

In FIG. 5 a gas separating system having a double column is diagrammatically shown, in which both components which are in thermal contact with one another in the condenser-evaporator, may be withdrawn frorn the system either in the gaseous state or the liquid state or in both these states.

In FIG. 6 a gas separating system according to FIG. 5

is shown, in which the column is so arranged as to make that a variation of the amounts of the discharge products does not affect in any respect the medium flows in the column. In FIG. 7 a gas separating system having a single column is diagrammatically illustrated, in which the product may be withdrawn from the system either in the gaseous state or in the liquid state or in both these states.

In FIGS. 1 to 4 inclusive the condenser-evaporator-part of a gas separating column is diagrammatically illustrated, in which the four different possibilities of the interconnection of the cooler-evaporator and the refrigerator are successively shown. In these figures the high pressure part of the gas separating column is indicated by 1 and the low pressure part thereof by 2. Provided between these two parts is a heat-exchanger 3, which is so arranged as to be adapted to collect in the liquid container 4 the liquid oxygen discharged from the column part 2. Below the heat exchanger 3 an annular container 5 is provided for collecting the condensed nitrogen. Connected to the liquid conta ner 4 is a liquid discharge conduit 6, whereas a liquid discharge conduit 7 is connected to the liquid container 5. Vapour discharge conduits 10 and 11 are connected to the vapour space 8 above the liquid container 4 and the vapour space 9 above the liquid container 5, respectively. The gas separating column contains also a cooler-evaporator 12, consisting of a container 13 which communicates through a liquid conduit 14 and a vapour conduit 15 with the condenser-evaporator. Provided in the container 13 is also a cooling coil 16, through which a portion of the gas mixture to be separated is passed and in which said mixture is cooled by condensed oxygen or nitrogen.

The system comprises further a cold-gasrefrigerator 17, which communicates through a conduit 18 with the vapour space which lies on one of the two sides of the heat-ex changer 3.

In FIG. 1 the container 13 of the cooler-evaporator is connected through the liquid conduit 14 with the liquid container 4, whereas the vapour conduit 15 opening into the upper part of the container 13 is connected to the vapour space 8 above the liquid container 4.1m this system the cooler-evaporator is connected in parallel with the evaporator of the column. The refrigerator 17 is connected by the conduit 18' with the vapour space 9 above the liquid container 5.

If only gaseous products are withdrawn from the gas separating system, these products are heated in the heatexchangers by thermal contact with the gas mixture to be separated. 1n that case the cold gas re fri'gerator has to supply only the cold which has been lost due to the heat exchange losses and the insulation losses. If the valves 19 and 20 provided in the liquid dlischarge conduits 6 and 7 are open, there will for instance .be discharged an amount p lonol/hr. of liquid oxygen through conduit 6 and an amount of p1 kniol/ hr. of liquid nitrogen through conduit 7. Since the total amount of product withdrawn from the system has to be kept constant, it will be apparent that through the vapour conduits 10 and 11 a quantity of gaseous oxygen which is p krnol/hr. less than before and a quantity of gaseous nitrogen which is 11 krnol/hr. less than before will be withdrawn, respectively;

In order to give a picture of the variations which occur owing to the discharge of liquid, it has been assurned that the amount of heat which must be with-drawn in order to cool 1 kmol of a substance from the surrounding temperature of the condensation temperature is about equal to the heat which must be withdrawn to condense 1 krnol of a gas which has been brought at the condensation temperature. This amount of heat is supposed to be equal to R kcal;

When the insulation losses and the heat exchange losses are neglected the cold-gas-refrigerator will have to substitute the amount of cold which has been discharged together with the liquid. The discharged amount of cold amounts in the present case 2(p +p )R kcal./hr., so that the cold-gas-refrigerator will have to condense an amount of 2(p +p kmol/hr. of gas.

Now, the cold-gas-refrigerator condenses a quantity of 2(p +p kmol/hr. more than before and this amount of condensate is supplied to the container 5. From this container the amount of p kmol/hr. of liquid gas is withdrawn, whereas from the space 9 an amount of gaseous nitrogen which pg kmolless than before is discharged. This means, that in the heat-exchanger 3 an amount of gas which is (212 4-17 kmol/hr. less than before has to. be condensed in order to keep the liquid level in the container 5 constant. This results in that in the container 4 an amount of gas which is (212 +p krnol/hr. less than before is evaporated. Through conduit 10 an amount of gas decreased by p krnol/hr. is withdrawn, whereas in order to keep the main heat exchangers balanced an amount of (p +p kmol/hr. of air to be separated is cooled in the coolercvaporator to about the condensation temperature and in the cooler-evaporator an amount of p +p ltmol/hr. of oxygen vapour is produced which is supplied to the space 8 through the conduit 15. Thus it is obtained that the vapour flow from the space 8 to the column part 2 is exactly equal .to the vapour flow under the circumstances when only gaseous products are withdrawn from the system. The only change is that the load of the heat-exchanger 3 has been decreased by the amount of 1+p2) I The same way of calculation may be applied to the other figures. For the sake of simplification of the specification these calculationshave been omitted and in the figures the flow variations are indicated in kmol/hr. From these flow variations the following facts appear:

(1) In the arrangement shown in FIG. 1 the load of the condenser-evaporator is decreased with the amount of P1-l-P2) p h i i u i .(2) In the arrangement shown in FIG. 2, in'yvhich the cold-gas-refrigerator is connected with the vapour space 8 above the liquid container 4, the load of the condenserevaporator is increased with the amount of p lgmol/ hr.

(3) In the arrangement illustrated in FIG. 3, which the cooler-evaporator 16 is connected in parallel with the liquid container 5 and the cold-gas-refrigerator com; municates with the vapour space 9 above the liquid container, the load or the condenser-evaporator is decreased with the amount of p kn'lol/ hr. i i

(4) In the arrangement shown in FIG. 4, in which the cooler-evaporator may be dispensed with by the combination of the cooler-evaporator and the condenser-evaporator-part of the column.

Of all above-mentioned arrangements the one shown in FIG. 1 is the most favorable one since:

(1) The evaporator-condenser is discharged with an amount of (2p +p kmol/hr.; this results in that,

when the system continuously delivers a great amount of its products in liquid state, the evaporator-condenser may be made smaller; and the same advantage is obtained, although to a smaller extent, with the arrangement shown in FIG. 3;

(2) The cold-gas-refrigerator condenses nitrogen in this system; the gas above the condenser-evaporator is mostly oxygen; in connection with the possible danger of explosion it is better to condense nitrogen in the refrigerator;

(3) The cold-gas-refrigerator condenses nitrogen at a raised pressure, say 5 atm., which may take place at a higher temperature than when nitrogen is condensed at atmospheric pressure; at this higher temperature the cold-gas-refrigerator operates with a better useful effect.

In the arrangement according to the invention the danger could occur that, when the gas mixture to be separated is passed at a raised pressure through the cooler-evaporator, this gas mixture is cooled to below its condensation temperature, so that already in the coil 16 condensation would start. To prevent this the cooler-evaporator may be constructed as shown in FIG. 4 in which the coolerevaporator has a second chamber, of which at least one wall is in thermal contact with the cold liquid contained in the container 13. The coil 16 provided in the second chamber communicates through a by-pass conduit 21 with the space in said chamber. Owing thereto the gas mixture to be separated condenses in the second chamber, so that the coil 16 is immersed in condensate of the gas mixture to be separated, whereby the temperature of the gas separating column is built of two parts 31 and 32. These densation temperature.

In FIG. 5 a gas separating system is installed which comprises a so-called double gas separating column. This gas separating column is built of two parts 31 and 32. These two parts are separated from one another by a heat-exchanger 33. This heat-exchanger 33 is so arranged as to be adapted to collect in the liquid container 34 the liquid oxygen discharged from the column part 32. Provided below the heat-exchanger 33 is an annular container 35 to collect the condensed nitrogen. Connected to the liquid container 35 is a liquid discharge conduit 36, in which a valve 37 is provided.

Connected to the liquid container 34 is a conduit 38 which connects the container 34 with the container 39. A discharge conduit 40 for liquid oxygen is connected to the lower side of the container 39 and it is provided with a valve 41. The upper part or" the container 39 communicates through a vapor conduit 42 with the space 43 above the liquid container 34. A container 44 is in thermal contact with liquid contained in the container 39 through a wall 45.

A conduit 46 for the discharge of gaseous oxygen is connected to the space 43.

A cold-gas-refrigerator 47 communicates through a conduit 48 with the space 49 above the liquid container 35. Also a conduit 50 for the discharge of gaseous nitrogen from the system is connected to the space 4?.

All discharge conduits 45, 50 and 51 for gaseous products pass through the main heat-exchanger 52, in which the gaseous products are in thermal contact with the air to be separated which is supplied to the system through the conduit 53. The conduit 53 is provided with a distribution valve 54 which, when a portion of the products is withdrawn from the system in liquid state, allows a portion of the air to be separated to flow through the conduit 55. This conduit 55 is followed by a heat-exchanger 56 contained in the container 44 and is thereafter followed by the conduit 57 which is connected to the lower part 31 of the column. A by-pass conduit 57' sees to it that the heatexchanger 56 is cooled with condensate of the gas mixture to be separated.

In addition conduits 58 and 59 are connected to the lower part 31 of the column, through which liquid from the lower part of the column is supplied as reflux to the upper part 32 of the column through heat-exchangers 60 and 61, respectively.

The operation of the system is as follows. When no liquid is discharged from the system, all cold withdrawn from the column by the gaseous products is regained in the heat-exchanger 52 by transmission to the air to be separated, at least when the losses of the heat-exchange are not taken into account. This means that in that case the cold-gas-refrigerator 47 has to substitute only the cold which has been lost by the heat-exchange and through the insulation. The distribution valve 54 is then so positioned as to prevent the air to flow through the conduit 55.

Now, should a quantity of p kmol/hr. of liquid oxygen be discharged when the valve 41 is opened, the following changes will occur. The liquid level in the container 34 will fall. A level indicator 64 provided in said container will alter the production of the cold-gas-refrigerator 47 in such a manner that the latter will condense a quantity which is an amount of p kmol/hr. more than before. Thereby an amount of gas which is p kmol/hr. less than before will be discharged from the column part 32. The amount of gas discharged through the discharge conduit 51 is kept constant by a valve 62 contained in said conduit. This means that through conduit 46 a quantity of gaseous oxygen decreased by p kmol/hr. will be discharged from the system. The result thereof is that the heat exchanger 52 will get unbalanced and that thereby the temperature will rise. This rise in temperature is measured by a tem perature sensitive element provided in the heat-exchanger which varies through a control device 63 the position of the distribution valve 54 in such a manner that less air will flow through the heat-exchanger 52 to the column part 31 and an amount of p kmol/hr. of said air will flow through conduit 55, heat-exchanger 56 and conduit 57 to the column part 31. Consequently, in the heat-exchanger 56 a quantity of p kmol/hr. of the air to be separated is cooled to its condensation temperature. Owing thereto an amount of p kmol/hr. of liquid oxygen will evaporate in the containers 39, 34. This results again in a fall of the liquid level in the container 34. The liquid indicator 64 controls the production of the cold-gas-re frigerator 47 in such a manner that the latter will produce an amount of liquid which is p kmol/ hr. more than before. Then a new state of balance has been reached, in which through a valve 41 a quantity of p kmol/hr. of liquid oxygen is discharged and through conduit 46 an amount of gaseous oxygen decreased by p kmol/hr. is withdrawn from the system whereas the cold-gas-refrigerator condenses an amount of gas which is 2p kmol/hr. more than first.

Should thereupon also valve 37 be opened, so that through said valve a quantity of p kmol/hr. of liquid nitrogen can leave the system, the following changes will occur. The level in the liquid container 35 falls, whereby less liquid is supplied over the brim of said container to the lower part 31 of the column. Due to that the temperature in the lower part of said column part will rise. This temperature is measured by means of a temperature sensitive element and the valve 67 provided in the discharge conduit 50 for gaseous nitrogen is adjusted through a control device 66 in such a Way that through said conduit an amount of gaseous nitrogen decreased by p;; kmol/ hr. can be discharged from the system. This means, that in the heat-exchanger 33 an amount of nitrogen increased by p kmol/hr. must be condensed. This has the result that in the liquid container 34 a quantity of liquid oxygen which is p kmol/ hr. more than first is evaporated, whereby the liquid level in said container falls. The liquid level indicator 64 then changes the production of the cold-gas refrigerator in such a manner that the latter will condense an amount of gas which is p kmol/hr. more than before.

Due to the fact that through conduit 50 a quantity of gas which is decreased by p;, kmol/hr. will be discharged, the heat-exchanger 52 will get unbalanced. The control device 63 will then readjust the distribution valve 54 so as to increase the supply of air to be separated to the column through conduit 55 and the cooler-evaporator by an amount of p kmol/hr. Consequently, in the heat-exchanging coil 56 a quantity of air which is increased with the amount of p kmol/hr. must be cooled to its condensation temperature, which results in the evaporation of a quantity of p kmol/hr. of liquid in the containers 39 and 34. The levels in the containers then fall and through the level indicator 64 the production of the cold-gas-refrigerator 47 is so varied that it again condenses an amount which is p kmol/ hr. more than before.

In the state of balance now obtained the system delivers a quantity of 17 kmol/hr. of liquid oxygen and a quantity of p kmol/hr. liquid nitrogen whereas a quantity of gaseous oxygen which is p, kmol/hr. less than before and a quantity of gaseous nitrogen which is 17 kmol/hr. less than before are withdrawn from the system. Then the cold-gas refrigerator condenses an amount of gas which is increased by 2(p +p kmol/hr., whereas the heat-exchanger 52 is completely balanced.

A small disadvantage of the gas-separating-system shown in FIG. 5 is that by opening the valve 37 not only liquid nitrogen is discharged but also the reflux-ratio in the lower part 31 of the column is temporarily changed. Due to this change a rise in temperature in said column part occurs which readjusts valve 67 through the controldevice 65.

In order to prevent this temporary change of the reflux-ratio, in FIG. 6 a gas-separating-installation is illustrated, in which the column is constructed in such a manner, that the withdrawal of liquid nitrogen does not affect the flow ratio in the lower part 31 of the column. The corresponding parts of this system and those shown in FIG. 5 have been indicated by the same reference numerals The only difierence is that the lower part 31 is connected through a conduit 69 with the container 35. Provided in the conduit 69 is a valve 70 which defines the intensity of the liquid flow towards the column part 31 and keeps said flow constant irrespective of the liquid level in the container 35. The column part 31 is also connected through a conduit 71 with the space 49 above the container 35.

When the valve 37 is opened, whereby liquid nitrogen discharged, the control cyclus occurring in the system is completely equal to that described in connection with FIG. 5.

When the valve 37 is opened, whereby liquid nitrogen is withdrawn from the system, the control is principally equal to that described in connection with FIG. 5. Only the valve 67 provided in the conduit 50, through which the gaseous nitrogen leaves the system, is now readjusted in accordance with the height of the liquid level in the container 35. This liquid level is measured by means of a liquid level indicator which controls through a control .device 73 the valve 67.

In the foregoing specification two systems have been described from which the two components can be withdrawn either in the gaseous state or in the liquid state or in both these states. The system according to the invention will be considerably simplified when only one pure product in the gaseous state and in the liquid state has to be Withdrawn from the system. An embodiment of such a system is diagrammatically shown in FIG. 7. The column used in this system is approximately equal to the upper part 32 of the column illustrated in FIG. 6. In the system shown in FIG. 7 the cooler-evaporator-device is entirely dispensed with and the cooling coil .56 is accommodated in the container 35.

When the valve 41 is opened liquid oxygen can be discharged from the system. In that case the level falls in container 34. The control device 64 will increase the production of the cold-gas-refrigerator. Thereby the quan' tity of gaseous oxygen leaving the system through conduit 46 is directl decreased. Then the heat-exchanger 52 gets y unbalanced. Control device 63 thereupon readjusts the distribution valve 54 in such a manner, that the heat-exchanger regains its balance. Then more gas mixture to be separated will flow through conduit 55 and cooling coil 56. In order to cool this increased amount of gas mixture more liquid evaporates in container 35. Due to that more vapour must be condensed in the condenser-evaporator which has the efiect that the liquid level in container 34 falls. The liquid level indicator 64 controls again the production of the cold-gas refrigerator in such a manner that the production is increased and a new state of balance is obtained.

What is claimed is:

1. Apparatus for the separation of air into nitrogen and oxygen components comprising, in combination,

an oxygen rectifying column and a nitrogen rectifying colum, each having a gaseous component outlet, and said columns being in thermal contact, a heat exchanger, means for passing all the gaseous components of said rectifying columns through said heat exchanger,

supply means for supplying a constant mass of air to be rectified which is equal to that amount capable of being cooled to condensation temperature in said heat exchanger when the outputs of said columns are solely gaseous, said supply means being connected to said columns through said heat exchanger and having a controllable by-pass in parallel with said heat exchanger,

means for selectively withdrawing an amount p kmol/ hr. of liquid component from one of said columns so that the gaseous component output from said one column is thereby reduced by p kmol/hn,

means responsive to withdrawal of said amount of liquid component for adjusting said by-pass to maintain the air passing from said heat exchanger at said condensation temperature,

means for cooling the by-pass' air to condensation temperture before separation in one of said columns by thermal contact with one liquid component of said columns,

and cold-gas refrigerator means responsive to said withdrawal of liquid component for withdrawing heat from one of said columns equal to that required to be withdrawn from said by-pass air in bringing it to said condensation temperature.

2. Apparatus for the separation by fractionation of a gas mixture, e.g. air, into two components, e.-g. a nitrogen product and an oxygen product and the production of at least one of these components in the liquid and in the gase- 011s state in any desired mass ratio, said apparatus comprising, in combination,

a pair of rectifying columns, a thermally conductive partition separating said columns and forming a liquid component evaporator space communicating with one column and a liquid component condensa-,

tion space communicating with the other column, a gaseous component outlet for each column and one of said columns having a liquid component outlet for controlled withdrawal of such liquid component,

means for supplying gas mixture to be separated to said columns and including parallel paths for such gas mixture,

a heat exchanger in one of said paths connected to said gaseous product outlets,

a second heat exchanger in the other of said paths in heat exchange relation to a liquid component of said columns,

means for controlling the relative amounts of incoming gas mixture flowing through said parallel paths in response and proportional to the amount of liquid component withdrawn through said liquid component Outlet,

and cold-gas-refrigerator means for cooling one of said columns in response and proportional to said amount of liquid component withdrawn.

3. An apparatus for the separation by fractionation of a gas mixture, e.g. air, into two components, egg. a nitrogen product and an oxygen product, and the production of each of said components in the liquid and in the gaseous state in any desired mass ratio, said apparatus comprising, in combination, two rectifying column chambers, a condensation compartment communicating with one of said column chambers and being partly a liquid container and partly a vapor space, an evaporation compartment communicating with the other one of said column chambers and being partly a liquid container and partly a vapor space, a thermally conductive partition separating said compartments and keeping the products produced in said compartments in thermal contact with one another, said condensation compartment, said evaporation compartment and said partition constituting together a condenser-evaporator which is provided between said column chambers, a cold-gas-refrigerator to supply the deficiency of cold lost by the discharge of liquid components from the apparatus, a cold head and a condensation chamber surrounding said cold head forming part of said cold-gas-refrigerator, said condensation chamber being directly connected with the vapor space of one of said compartments of the condenser-evaporator, a conduit for the supply of gas mixture to be separated to the apparatus, a first heat-exchanging system connected to said supply conduit, said column chambers and said condensepevaporator, all components discharged from the apparatus in the gaseous state and at least part of the supplied gas mixture being individually passed through said heat-exchanging system in thermal contact with one another, a cooler-evaporator forming a second heat-exchanging system, an evaporation space and a cooling space contained in said cooler-evaporator, the lower part and the upper part of the evaporation space of said cooler-evaporator being connected to the liquid container and the vapor space of one of the compartments of the condenser-evaporator, respectively, a conduit from one of said columns connecting the cooling space of said cooler-evaporator with a conduit by-passing the first heatexchanging system connected to said supply conduit for the gas mixture and means to so divide the supply of gas mixture over both heat-exchanging systems as to keep the first heat-exchanging system in thermal balance.

4. In an apparatus as claimed in claim 3, the evapora- 10 tion space of the cooler-evaporator and the cold-gas-refrigerator being connected to difierent compartments of the condenser-evaporator.

5. In an apparatus as claimed in claim 3 the evaporation space of the cooler-evaporator and the cold-gas-refrigerator being connected to different compartments of the condenser-evaporator.

6. In an apparatus as claimed in claim 5 the evaporation space of the cooler-evaporator being connected to the evaporation compartment and the cold-gas-refrigerator being connected to the condensation compartment of the condenser-evaporator.

7. In an apparatus as claimed in claim 3 the provision of control means adapted to vary the output of the coldgas-refrigerator and the ratio of the medium flows in the apparatus in accordance both with the amount of cold lost by the discharge of liquid components from the apparatus and with the ratio of the quantities of gaseous and liquid components discharged from the apparatus so as to keep the heat-exchanging systems in balance.

8. In an apparatus as claimed in claim 7 the provision of an indicator to indicate the liquid level in the evaporation compartment of the condenser-evaporator and a regulator to control the output of the cold-gas-refrigerator said level indicator being operationally connected to said regulator in order to increase the output of the cold-gas refrigerator at a fall of the meant liquid level and vice versa.

9. An apparatus as claimed in claim 7, in which the control means are adapted to so vary the amounts of discharged gaseous components in accordance with the amounts of discharged liquid components as to keep the total mass of each component discharged from the apparatus constant.

References Cited UNITED STATES PATENTS 2,650,482 9/1953 Lobo 62-15 X 2,664,719 1/1954 Rice et al 6229 X 2,808,709 10/1957 Kohler 62--92 X 2,975,606 3/ 1961 Karwat.

3,237,418 3/ 1966 Meisler 62-92 X 3,210,950 10/1965 Lady 6213 X 3,246,478 4/1966 Kornemann et al. 62-29 X NORMAN YUDKOFF, Primary Examiner. V. W. PRETKA, Assistant Examiner. 

1. APPARATUS FOR THE SEPARATION OF AIR INTO NITROGEN AND OXYGEN COMPONENTS COMPRISING, IN COMBINATION, AN OXYGEN RECTIFYING COLUMN AND A NITROGEN RECTIFYING COLUMN, EACH HAVING A GASEOUS COMPONENT OUTLET, AND SAID COLUMNS BEING IN THERMAL CONTACT, A HEAT EXCHANGER, MEANS FOR PASSING ALL THE GASEOUS COMPONENTS OF SAID RECTIFYING COLUMNS THROUGH SAID HEAT EXCHANGER, SUPPLY MEANS FOR SUPPLYING A CONSTANT MASS OF AIR TO BE RECTIFIED WHICH IS EQUAL TO THAT AMOUNT CAPABLE OF BEING COOLED TO CONDENSATION TEMPERATURE IN SAID HEAT EXCHANGER WHEN THE OUTPUTS OF SAID COLUMNS ARE SOLELY GASEOUS, SAID SUPPLY MEANS BEING CONNECTED TO SAID COLUMNS THROUGH SAID HEAT-EXCHANGER AND HAVING A CONTROLLABLE BY-PASS IN PARALLEL WITH SAID HEAT EXCHANGER, MEANS FOR SELECTIVELY WITHDRAWING AN AMOUNT P1 KMOL/ HR. OF LIQUID COMPONENT FROM ONE OF SAID COLUMNS SO THAT THE GASEOUS COMPONENT OUTPUT FROM SAID ONE COLUMN IS THEREBY REDUCED BY P1 KMOL/HR., MEANS RESPONSIVE TO WITHDRAWAL OF SAID AMOUNT OF LIQUID COMPONENT FOR ADJUSTING SAID BY-PASS TO MAINTAIN THE AIR PASSING FROM SAID HEAT EXCHANGER AT SAID CONDENSATION TEMPERATURE, MEANS FOR COOLING THE BY-PASS AIR TO CONDENSATION TEMPERATURE BEFORE SEPARATION IN ONE OF SAID COLUMNS BY THERMAL CONTACT WITH SAID LIQUID COMPONENT OF SAID COLUMNS, AND COLD-GAS REFRIGERATOR MEANS RESPONSIVE TO SAID WITHDRAWAL OF LIQUID COMPONENT FOR WITHDRAWING HEAT FROM ONE OF SAID COLUMNS EQUAL TO THAT REQUIRED TO BE WITHDRAWN FROM SAID BY-PASS AIR IN BRINGING IT TO SAID CONDENSATION TEMPERATURE. 